The crucial roles of activation fragments of C3 which lead to cytolysis of malignant cells has been demonstrated in cell-mediated and humoral immune responses. In these processes regulation of the enzymatic activity of the C3b-dependent C3 convertase (C3bBb) is a key step in the initiation of the effector system directed at elimination of neoplasia by the host. The research objectives outlined in this proposal will attempt to assess the biological and functional properties of the active subunit of this C3 convertase (Bb) in terms of its biochemical structure. This information is essential to fully comprehend the mechanism of action of this enzyme, its interaction with C3b and its relevance to other gene products coded by the major histocompatibility complex which may share similar structural and immunochemical properties. Factor B will be utilized during the project period to: a) elucidate a major portion of its amino acid sequence, b) explore and localize the substrate-binding site, c) examine the nature of its genetic polymorphism, d) identify functional peptides which are responsible for CVF and C3b binding, and e) ascertain common structural features with C2 of the classical pathway. A variety of chemical and enxymatic cleavage techniques will be examined in order to optimize the generation of peptides. High-pressure liquid chromatography and microsequence technology will facilitate and expedite the isolation, sequencing, and alignment of individual peptide fragments. Is is anticipated that these investigations will provide new and important information on the mechanism of activation of factor B and C3. Such data will be useful in devising effective therapy to control inflammation and thus the extent of necrosis associated with a number of human diseases including myocardial infarction, rheumatoid arthritis, systemic lupus erythematosis, malaria, schistasamiasis, and viral diseases in which the complement system is known to be damaging. Moreover, the results of the these studies would also enhance our understanding of other metabolic functions associated with complement activation such as chemotaxis, opsonization, lymphocyte stimulation, immune adherence, and regulation of macrophage functions.